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From Nikhil Chhaochharia <>
Subject Re: Multiple Indices vs Single Index
Date Thu, 20 Sep 2007 15:16:58 GMT
I am sorry, it seems that I was not clear with what my problem is.  I will try to describe
it again.

My data is divided into 40 categories and at one time only one category can be searched. 
The GUI for the system will ask the user to select the category from a drop-down.  Currently,
I have a separate index for every category.  The index sizes varies - one category index is
10MB and another is 700MB.  Other index-sizes are somewhere in between.

I was wondering if it will be better to just have 1 large index with all the 40 indices combined.
 I do not need to do dual-queries and my total index size (if I create a single index) is
about 3.4GB.  It will increase to maximum of 5-6 GB.  I am running this on a dedicated machine
with 8GB RAM.

Unfortunately I do not have enough hardware to run both in parallel and test properly.  Have
just one server which is being used by live users.  So it would be great if you could tell
me whether I should stick with my 40 indices or combine them into 1 index.  What are the pros
and cons of each approach ?


----- Original Message ----
From: Grant Ingersoll <>
Sent: Thursday, 20 September, 2007 7:57:21 PM
Subject: Re: Multiple Indices vs Single Index

If I understand correctly, you want to do a two stage retrieval  
right?  That is, look up in the initial index (3.4 GB) and then do a  
second search on the sub index?  Presumably, you have to manage the  
Searchers, etc. for each of the sub-indexes as well as the big  
index.  This means you have to go through the hits from the first  
search, then route, etc. correct?

Have you tried creating one single index with all the (stored)  
fields, etc?  Worst case scenario, assuming 1GB per index, is you  
would have a 40GB index, but my guess is index compression will  
reduce it more.  Since you are less than that anyway, have you tried  
just the straightforward solution?  Or do you have other requirements  
that force the sub-index solution?  Also, I am not sure it will work,  
but it seems worth a try.  Of course, this also depends on how much  
you expect your indexes to grow.

Also, what was inconclusive about your tests?  Maybe you can describe  
more what you have tried to date?


On Sep 20, 2007, at 3:50 AM, Nikhil Chhaochharia wrote:

> Hi,
> I have about 40 indices which range in size from 10MB to 700MB.   
> There are quite a few stored fields.  To get an idea of the  
> document size, I have about 400k documents in the 700MB index.
> Depending on the query, I choose the index which needs to be  
> searched.  Each query hits only one index.  I was wondering if  
> creating a single index where every document will have the  
> indexname as a field will be more efficient.  I created such an  
> index and it was 3.4 GB in size.  My initial performance tests with  
> it are not conclusive.
> Also, what are the other points to be addressed while deciding  
> between 1 index and 40 indices.
> I have 8GB RAM on the machine.
> Thanks,
> Nikhil
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Grant Ingersoll

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